1. Field of the Invention
This invention relates to a semiconductor fabrication method, and more particularly, to a method of fabricating resistors in integrated circuits.
2. Description of Related Art
Resistors are the most often used components in all kinds of electrical and electronic circuits, including integrated circuits such as memory and logic devices. Conventionally, resistors in integrated circuits are made from lightly-doped polysilicon layers that are shaped into specific lengths and cross-sectional areas to provide the desired resistance values. Another conventional method of forming resistors in integrated circuits is to perform a thermal annealing process on a joined structure of a high-resistance conductive layer and a low-resistance conductive layer, such as an undoped polysilicon layer and a highly-doped polysilicon layer. This method also requires the conductive layers to be shaped into specific lengths and cross-sectional areas to provide the desired resistance values.
Patents that disclose methods of fabricating resistors in integrated circuits include the U.S. Pat. No. 5,316,978 entitled "Fabricating Resistors for Integrated Circuits", the U.S. Pat. No. 5,465,005 entitled "Polysilicon Resistor Structure Including Polysilicon Contact", and the U.S. Pat. No. 5,677,228 entitled "Method of Fabricating a Resistor in an Integrated Circuit", to name just a few.
One drawback to the above-mentioned methods, however, is that, since polysilicon is used to form the resistors, the method requires the use of an etching process to shape the polysilicon layers into specific lengths and cross-sectional areas to provide the desired resistance values. This makes the overall process quite complex and thus laborious to carry out. Still another drawback is that the use of polysilicon allows only a limited range of resistance values for the resultant resistors. This is because the resistance of a polysilicon-based resistor is largely dependent on the length and crosssectional area of the resistor. A high resistance therefore requires that the polysilicon layer be very long. Since a wafer is very small in size, the feasible range of resistance values for the resultant resistors is limited.